In modern (wireless and/or cellular) communication systems, such as e.g. LTE and LTE-A and its successors, multiple-input multiple-output (MIME) systems, including single-user (SU-) and multi-user (MU-) MIMO systems, are gaining increasing attention and importance. Such MIMO systems are typically sensitive to network performance limitations in view of (e.g. inter-cell) interference, especially at cell edges.
Coordinated multi-point (CoMP) transmission/reception operations are adopted as a technique for improving coverage of high data rates, cell-edge through put/performance, and system throughput/performance. In downlink CoMP operations, multiple points (which in practice may typically be base stations, remote radio heads, access nodes or the like) co-operate in scheduling and transmission of downlink communications in order to strengthen a desired signal and mitigate inter-cell interference. In this regard, a point is regarded as a set of geographically co-located transmit antennas at one site, and a site including a plurality of sectors has a corresponding plurality of different points, each corresponding to a given sector of the site. A cell may be formed by one or multiple points, meaning that one cell can include transmit antennas co-located at a single geographical location and/or distributed over multiple geographical locations.
In terms of CoMP, intra- and inter-cell downlink COMP operations in homogeneous and heterogeneous network deployments are specifically considered.
In the context of CoMP operations, various CoMP schemes (also referred to as CoMP categories) are considered. Such CoMP schemes include joint transmission (JT), dynamic point selection (DPS), and coordinated scheduling/beamforming (CS/CB). In joint transmission (JT) CoMP, two or more points transmit simultaneously to a CoMP user. Dynamic point selection (DPS) refers to a CoMP scheme where the transmission point is switched according to changes in channel and interference conditions. In coordinated beamforming/scheduling (CB/CS) CoMP, the scheduling decisions of neighbor points are coordinated in order to reduce interference. In principle, all of these CoMP schemes may include dynamic point blanking/muting which means that one or more transmission points are blanked/muted (i.e. turned off) to decrease interference.
Further, in the context of CoMP operations, various CoMP scenarios are considered. Such CoMP scenarios include an intra-site scenario (in a homogeneous network) where multiple co-located sectors of the same base station site are cooperating (referred to as scenario 1), an inter-site scenario (in a homogeneous network) with high power remote radio heads (RRH) where multiple non-co-located points having the same transmit power are cooperating (referred to as scenario 2), a heterogeneous network scenario with low power RRHs within the coverage of a high power macro cell, each operating in/as its own cell (referred to as scenario 3), and a heterogeneous network scenario with low power RRHs within the coverage of a high power macro cell, each operating in/as the same cell (referred to as scenario 4). The above stated list of CoMP scenarios is not to be understood as being exhaustive. Other CoMP scenarios may be envisioned.
Generally, CoMP operations rely on feedback. Namely, a CoMP transmission point typically relies on channel state information (CSI) feedback from a CoMP user. In downlink CoMP operations, such CSI feedback is provided in the uplink direction from a terminal or user equipment (UE) serving as the CoMP user to a base station, access node, evolved NodeB (eNB), or the like serving as the CoMP transmission point.
For the different CoMP schemes mentioned above, different types and/or contents of CSI feedback are effective or required for the CoMP transmission point so as to perform the respective CoMP scheme in an efficient and appropriate manner.
In view thereof, when CoMP operations are implemented in a variety of CoMP schemes and/or CoMP scenarios, there is a problem in identifying when providing CoMP CSI feedback is more appropriate than providing per-point CS feedback with respect to CoMP controller entity for supporting a given CoMP operation. It is noted that transmission of CoMP feedback uses UL resources. If CoMP will not be used by the base station, e.g. in the initial stage or when exiting CoMP mode, no benefit is gained from using the UL resources for CoMP feedback.
Accordingly, there is a desire or even need to realize a feedback indicator for coordinated multi-point operations of various coordinated multi-point schemes and/or scenarios.